The image of a parabolic mirror is sketched on a graph. The image can be represented using the function y is equal to negative 1 eighth x squared plus 2 , where x represents the horizontal distance from the maximum depth of the mirror and y represents the depth of the mirror as measured from the x -axis. How far away from the maximum depth is a point on the mirror that is 7 eighths inches in depth?
Set the depth y equal to 7/8: 7/8 = −(1/8)x² + 2. Multiplying by 8 gives 7 = −x² + 16, so x² = 9 and x = ±3. The point is 3 inches from the maximum depth, so the correct choice is C, 3 inches.
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